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Disease Focus: Escherichia coli

Food Borne Illnesses

in the United States

by Jennifer Villegas

Health Implications of Escherichia coli in Recreational and Drinking Water

by Lori Lewis

Escherichia coli, commonly referred to as E. coli, is a member of a group of organisms known as coliforms: common bacteria found in the digestive system of humans and animals. This organism is usually not a cause for concern, as there are only a few strains that cause serious disease in humans. One of these strains is responsible for causing Traveler’s diarrhea, and the second is E. coli O157:H7, which contaminates meat and leafy vegetables. This strain (O157:H7) can cause serious hemorrhagic diarrhea and can have long term, if not fatal, complications.

The presence of E. coli is used as an indicator to monitor the possible presence of other more harmful microbes, such as Cryptosporidium, Giardia, Shigella, and norovirus. Some possible sources of fecal contamination include: agricultural runoff, wildlife that uses the water as their natural habitat, runoff from areas contaminated with pet manure, wastewater treatment plants, and on-site septic systems. Heavy precipitation may cause these organisms to be washed into creeks, rivers, streams, lakes, or ground water. If this water is used as a source of drinking water and is not treated, or is inadequately treated, it may result in illness.

Diseases acquired from contact with contaminated water can cause gastrointestinal illness, skin, ear, respiratory, eye, neurologic, and wound infections. The most commonly reported symptoms are stomach cramps, diarrhea, nausea, vomiting, and low-grade fever.

When E. coli exceeds the permissible level in recreational water, it results in the closing of beaches, ponds, lakes, and swimming and fishing areas. There are lower thresholds for levels of bacteria in drinking water from public water systems, which have been set by the Safe Drinking Water Act. If this level is reached or exceeded, consumers are advised to boil water they use for cooking, drinking, making baby formula, and for brushing teeth.

However, a large portion of the US population uses groundwater that is not regulated by the Safe Drinking Water Act because the water comes from private wells. Although not regulated by the EPA, there are resources available on their website for monitoring and maintaining private wells.

E.coli Contamination

by Saima Hedrick

Escherichia Coli (E. coli) is a bacterium that inhabits the intestinal tracts of warm-blooded animals and can live outside of the intestine for a short period of time. Excreted waste of these animals is teeming with E. coli, which can be transferred to nearby water and food if the waste is not properly disposed. Testing water and food supplies for this organism, and others in the coliform group, can indicate whether or not there has been recent fecal contamination. 

The EPA requires that all water be tested for coliforms and has a zero tolerance policy. This means that water that tests positive for coliforms must be tested again and, if found to be positive again, is deemed impaired. If this water is consumed before it can be treated, it can cause severe diarrhea, vomiting, and cramps. In immune compromised subjects, the resulting infection can be fatal. The same is true if E. coli contaminated food is eaten without being properly cooked to kill off pathogens.

Although E. coli contamination from human waste elicits the most disgust in the populous, it is not the most pathogenic to humans. In the United States, most of the strains detected in food and the water are traced back to livestock such as cows, pigs, and sheep. E. coli can also be found in the waste of wildlife such as waterfowl, deer, and raccoons.

Watershed efforts focus on runoff from livestock, but park areas with flocks of geese can lead to serious E. coli contamination of local waterways. Feeding the geese not only disrupts their natural diet, but also causes them to linger in the area, increasing the amount of goose droppings. Children playing in these areas are then at risk for exposure, and there is more waste in the runoff.

In more urban areas, pet waste is becoming a major issue. Unbagged pet waste can wash into the waterways. According to an article on protecting the Chesapeake Bay watershed, in a 20-square-mile watershed, “two to three days of droppings from a 100 dogs would contribute enough E.coli bacteria to temporarily close the bay to swimming”.

These wildlife sources of E. coli are difficult to track, making it harder to correct the problem. Local stream monitoring efforts can help triangulate where the E. coli is coming from but these efforts are not frequent as they take much more time, and therefore funds, than the local government can afford. Moreover, the human dimension of feeding geese and cleaning up pet waste is difficult to target. Dog bag stations are provided in many park areas and yet the waste is still left behind.

Overall, E. coli contamination is a problem that has many sources. As the local governments provide better resources to remedy this problem, we humans need to recognize that we are contributors to the problem and must therefore be part of the solution.

For more information, contact Saima at

e. Coli

Coliscan Testing Media for e.Coli in Recreational Waters

By Piper Wilson

Coliscan media is a patented combination of color-producing chemicals and nutrients that detect coliforms and E. coli in specific colors for an easy identification and isolation. Meaning that a water sample may be added to the medium, and coliform bacteria will grow in either pink-magenta colonies or in purple-blue colonies, signifying E. coli. Generally other bacterial types will grow as non-colored colonies. There are two approaches to the Coliscan method, Coliscan Easygel and Coliscan MF.

When a sample size is of 1-5 mL, the Coliscan Easygel is ideal. An example of this would be the testing of river waters or other samples where there is normally a considerable amount of coliforms and E. coli. The sample can be added directly into the bottle of Coliscan Easygel, swirled, poured into a pretreated petri dish, incubated, and results can be read in 24-28 hours.

Normally, coliforms are found in soil and water and do not necessarily point towards the presence of fecal contamination, but Escherichia coli (E. coli) is a major bacterium in the human and animal intestinal tract and its presence in food or water indicates fecal contamination. The USEPA, United States Environmental Protection Agency, acknowledges that E. coli is the best sign of a health risk in fresh water and currently recommends testing for E. coli.

The other approach to testing for E. coli is using Coliscan MF, or a membrane filter. This is used with membrane filters, and it allows for much larger test samples of any filterable liquid. Coliscan MF is commonly used with potable water or treated wastewater that contains low levels of coliforms or E. coli. The steps to this approach include, the sample being filtered through a membrane filter, the bacteria become collected on the surface of the filter, it is then placed on a pad saturated with Coliscan MF liquid medium in a petri dish, where the colonies grow on the surface of the filter and are then they are counted.

If coliform colonies are present, a water insoluble pink pigment will be produced due to the enzyme galactosidase reacting with the colony and substrate. Therefore only deep blue-purple colonies are counted as E. coli.

Coliscan has numerous advantages over the other methods for water testing. It gives a simple, accurate and quantitative way to identify and differentiate coliforms and E. coli from other bacteria in water. It has a shelf life of 1 year and should be kept frozen until used.

testing for e.Coli

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